Published online 15 June 2011 | Nature 474, 272-274 (2011) | doi:10.1038/474272a
News Feature
Physics of life: The dawn of quantum biology
Philip Ball
The key to practical quantum computing and high-efficiency solar cells may lie in the messy green world outside the physics lab.
On the face of it, quantum effects and living organisms seem to occupy utterly different realms. The former are usually observed only on the nanometre scale, surrounded by hard vacuum, ultra-low temperatures and a tightly controlled laboratory environment. The latter inhabit a macroscopic world that is warm, messy and anything but controlled. A quantum phenomenon such as 'coherence', in which the wave patterns of every part of a system stay in step, wouldn't last a microsecond in the tumultuous realm of the cell.
Or so everyone thought. But discoveries in recent years suggest that nature knows a few tricks that physicists don't: coherent quantum processes may well be ubiquitous in the natural world. Known or suspected examples range from the ability of birds to navigate using Earth's magnetic field to the inner workings of photosynthesis — the process by which plants and bacteria turn sunlight, carbon dioxide and water into organic matter, and arguably the most important biochemical reaction on Earth.
Biology has a knack for using what works, says Seth Lloyd, a physicist at the Massachusetts Institute of Technology in Cambridge. And if that means "quantum hanky-panky", he says, "then quantum hanky-panky it is". Some researchers have even begun to talk of an emerging discipline called quantum biology, arguing that quantum effects are a vital, if rare, ingredient of the way nature works. And laboratory physicists interested in practical technology are paying close attention. "We hope to be able to learn from the quantum proficiency of these biological systems," says Lloyd. A better understanding of how quantum effects are maintained in living organisms could help researchers to achieve the elusive goal of quantum computation, he says. "Or perhaps we can make better energy-storage devices or better organic solar cells."
Energy routefinder
Researchers have long suspected that something unusual is afoot in photosynthesis. Particles of light called photons, streaming down from the Sun, arrive randomly at the chlorophyll molecules and other light-absorbing 'antenna' pigments that cluster inside the cells of every leaf, and within every photosynthetic bacterium. But once the photons' energy is deposited, it doesn't stay random. Somehow, it gets channelled into a steady flow towards the cell's photosynthetic reaction centre, which can then use it at maximum efficiency to convert carbon dioxide into sugars.
Since the 1930s, scientists have recognized that this journey must be described by quantum mechanics, which holds that particles such as electrons will often act like waves. Photons hitting an antenna molecule will kick up ripples of energized electrons — excitons — like a rock splashing water from a puddle. These excitons then pass from one molecule to the next until they reach the reaction centre. But is their path made up of random, undirected hops, as researchers initially assumed? Or could their motion be more organized? Some modern researchers have pointed out that the excitons could be coherent, with their waves extending to more than one molecule while staying in step and reinforcing one another.
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Read more here/Leia mais aqui: Nature
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